Process control systems, like those used in chemical, petroleum or other processes, typically include a centralized process controller communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses. The field devices, which may be, for example valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process such as opening or closing valves and measuring process parameters. The process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine and then generates control signals which are sent over the buses to the field devices to control the operation of the process. Information from the field devices and the controller is typically made available to one or more applications executed by the operator workstation to enable an operator to perform any desired function with respect to the process, such as viewing the current state of the process, modifying the operation of the process, etc.
In the past, conventional field devices were used to send and receive analog (e.g., 4 to 20 milliamp) signals to and from the process controller via an analog bus or analog lines. These 4 to 20 ma signals were limited in nature in that they were indicative of measurements made by the device or of control signals generated by the controller required to control the operation of the device. However, in the past decade or so, smart field devices including a microprocessor and a memory have become prevalent in the process control industry. In addition to performing a primary function within the process, smart field devices store data pertaining to the device, communicate with the controller and/or other devices in a digital or combined digital and analog format, and perform secondary tasks such as self-calibration, identification, diagnostics, etc. A number of standard and open smart device communication protocols such as the HART®, PROFIBUS®, WORLDFIP®, Device-Net®, and CAN protocols, have been developed to enable smart field devices made by different manufacturers to be used together within the same process control network. More recently smart field devices have been equipped with wireless transceivers, allowing the smart field devices to communicate wirelessly with process controllers and applications executed on various operator workstations within the process plant environment. Various wireless communication protocols, such as the HART wireless communication protocol, have been developed to facilitate wireless communications between wireless enabled process control devices or other process control equipment and process controllers, operator workstations, and the like.
Once installed, process control devices are subject to operational wear and tear, and over time may be subject to failure. In order to minimize process downtime resulting from unpredicted device failures, it is desirable to maintain an inventory of spare process control field devices so that when a failure does occur replacement parts are readily available. Managing such an inventory can present a number of challenges. Each field device must be individually identified and must meet certain specifications to ensure that it is capable of performing the specific process control function for which it is intended. An instrumentation department of even a medium-sized processing plant may include between 3,000 and 6,000 field devices. Keeping track of all the field devices in such an environment, monitoring an inventory of spare parts, ordering replacement field devices, and receiving and inspecting received field devices can be a monumental task.
Particularly burdensome is the task of inspecting received field devices and other equipment to ensure that the received devices meet specified requirements. In the past, this has required unpacking each individual process control field device when it is received and physically inspecting the field device to ensure compliance with specified requirements. This can be very time consuming and can be prone to errors if the personnel inspecting the received field devices happen to miss discrepancies between the specified device and the device actually received.
The advent of smart process control field devices has alleviated this problem to a degree. Smart process control field devices may be shipped with specification data stored in the smart process control field device's internal memory. The specification data stored in the device describe the device and how it is configured. The specification data stored in the device memory may include for example, a device tag identifying the device, various operating parameter values describing operating ranges, capacity, sizes, materials of construction, and types of sensors associated with the device as shipped from the supplier. In fact, the data stored in the device memory may include all of the specifications used for ordering the device.
When the smart process control field device is received at the processing plant, receiving personnel may connect the device to an inspection fixture adapted to read the device data from the received device's internal memory. An inventory control application associated with the inspection fixture may have access to a database storing the specification data for the field devices used throughout the process plant environment. The inventory control application may then compare the device data read from the device memory to the specification data stored in the database for the device to ensure that the received smart process control field device was configured and shipped according to the device specifications. While this semi-automated procedure has advantages over a purely manual inspection by plant receiving personnel, it still requires that devices be at least partially unpacked and individually connected to a test fixture. This can be inconvenient and time-consuming, especially when hundreds or thousands of process control field devices are received on a regular basis.
Another difficulty in maintaining an up-to-date inventory of process control field devices is tracking specification changes for individual process control field devices. Over time the specifications for various process control field devices may be altered to improve process performance or for other reasons. Such changes may be the result of design changes, or the introduction of newer devices that provide some improvement in performance or cost savings over the originally specified devices. Such changes must be reflected in the purchase orders issued for the replacement process control field devices whose specifications have changed. Complicating things further is the fact that specifications might be changed after an order has already been placed for a replacement process control device, or even after replacement devices have already been received at the process plant and placed in inventory. In this case, it is undesirable to replace an existing process control device with a spare device that is configured according to outdated specifications.
A final challenge in maintaining an inventory of replacement process control field devices is one of simple accounting. Keeping track of all of the process control field devices in a process plant, including both installed field devices and spare field devices held in inventory, can be complicated and time consuming. Monitoring the inventory is necessary, however, in order to ensure that adequate replacement parts are available so that, if a field device fails or is coming to the end of its expected operational life, the failed or aging field device may be replaced with as little interruption to the controlled process as possible.